1. Field of the Invention
This invention relates to an autonomous control system for small unmanned helicopters, and autonomous control algorithms that control rudders for said small unmanned helicopter based on the aforementioned mathematical models.
2. Description of the Prior Art
Helicopters are flying bodies that have operating ranges such as longitudinal motions, lateral motions, vertical motions, and hovering, which are not exhibited by an aircraft; as such, they have the advantage of being able to flexibly respond to various situations.
This advantage has led to the expectation of the construction of small, unmanned helicopters for use in places that are difficult or dangerous for manned operations, for example in high-altitude work, such as the inspection of power transmission lines, or in emergency rescue operations or the detection of land mines. Previously, an autonomous control system using an unmanned helicopter for agricultural chemical spray applications was described in Patent Reference 1, i.e. Patent Disclosure 2000-118498
First, let us provide a logical explanation of the mechanism of autonomous control for helicopters. Helicopters are the objects of control; they are flying bodies that are capable of changing their orientation by means of servo motor actions and are capable of three-dimensional motions. The purpose of flying by autonomous control is to move the helicopter according to positional and speed target values. The required maneuvering follows the computational results generated by calculation computer. In order to delegate the piloting of a helicopter to a computer, the calculation computer must have sensing and actuation functions. Devices that have the function of sensing the various flight conditions of a helicopter are called sensors. Actuators that move the helicopter's rudders by receiving autonomous control signals that are generated by determining control reference values based on computational results from the computer and by converting these results into signals are referred to as servo motors. The helicopter can be autonomously controlled toward a given target value by means of a feedback control loop that links “(sensor)—(calculation computer)—(servo motor)—(helicopter), Reference FIG. 1”.
Following is a description of autonomous control for a small unmanned helicopter described in Patent Reference 1, with reference FIG. 2 to drawings. This system can be divided into a mobile station, which includes the helicopter and a ground station. Mounted on the ground station are a helicopter body 101; a sensor 102 that detects the current position and attitude angle of the helicopter body 101; servo motors 103 that move the rudders for the helicopter body 101; a backup receiver 104 that receives manual maneuver signals from a backup transmitter 110; and a wireless modem that communicates with the ground station. Employed in the sensor 1021 are the GPS (not shown in the figure) that detects the current position of the helicopter body 101 and tri-axis orientation sensors (not shown in the figure) that detect the tri-axial attitude angles of the helicopter body 101. Installed on the ground station are a computer CPU 108 for the input of reference values on which speed reference values are entered; a computer CPU 109 for internal computation purposes; and a backup transmitter 110 that permits the operator to perform manual operations in the event of the occurrence of a dangerous situation. The CPU 109 calculates position and attitude angle reference values from target speed values, compares the results with the current position, speed, and attitude angle obtained from the sensors 102, and based on these results, calculates control instruction values that bring the helicopter to the reference values. By forming a feedback control loop by linking “(sensors 102)—(CPU 109)—(servo motors 103)—(helicopter body 101)” (intervening components omitted), it is possible to effect the autonomous control of the helicopter toward its reference values.
Following is a description of the operation of the system. The operator sets four speed reference values (Vx*, Vy*, Vz*, ω*) consisting of longitudinal, lateral, vertical, and rotational speeds, on the CPU 58. The CPU 59 integrates these speed reference values with respect to time, obtaining a longitudinal target position X*, a lateral target position Y*, a vertical target position Z*, and a rotational target position (yawing angle) ψ*. Similarly, the CPU 59 differentiates the four speed reference values (Vx*, Vy*, Vz*, ω*) and multiplies the results by coefficients to calculate a target pitching angle θ* and a target rolling angle φ*. The differences between the target values that are set in this manner and the detected values (θ, φ, ψ, ω) for the body attitude, speed (X, Y, Z, Vx, Vy, Vz) that are detected by the sensors 52 consisting of the GPS and tri-axis attitude sensors that are installed on the helicopter body 51 are calculated as follows:ΔX=X*−X ΔY=Y*−Y ΔZ=Z*−Z ΔVx=Vx*−Vx ΔVy=Vy*−Vy ΔVz=Vz*−Vz Δθ=θ*−θΔφ=φ*−φΔψ=ψ*−ψΔω=ω*−ω
Based upon these differences (errors), the CPU 109 calculates control reference values for the servo motors 103 that move the rudders for the helicopter body 101. Four types of control reference values are computed: elevator servo (longitudinal) instruction, aileron servo (lateral) instruction, corrective servo (vertical) instruction, and rudder servo (rotational) instruction. After computing these four types of control reference values, the CPU 109 supplies them to the aforementioned servo motors 103, and performs feedback control on these operations until the differences become zero (0).
Helicopters that are used in the aforementioned conventional autonomous control system were originally intended for the spraying of agricultural chemicals, with a maximum weight of approximately 30 kg. Although the aforementioned sensors and computational unit for the aforementioned conventional autonomous control system are large and heavy, the helicopter can adequately fly even when carrying these items. The unloaded helicopter used in the aforementioned conventional autonomous control system weighs approximately 60 kg, and approximately 90 kg when fully loaded. Therefore, such a helicopter cannot easily be carried. In addition, in order to use the system, the helicopter must have a flight range sufficiently larger than the actual helicopter, which limits the range over which the helicopter can be deployed. In some cases, manned helicopter operations involve a narrow space in which the aforementioned conventional helicopter cannot negotiate. On the other hand, the small unmanned helicopter of the present invention refers to a helicopter that is comparable to, and compatible with, commercially available hobby small-scale radio-controlled helicopters in size and weight.
Although the above problem can be solved by effecting autonomous control in such a helicopter, the smaller the weight of a helicopter, the more difficult it is to control. In other words, the autonomous control system is subject to stringent constraints in terms of size and weight, and small helicopters tend to be unstable in terms of dynamical properties. Therefore, with the aforementioned conventional autonomous control system, it is impossible to mount the autonomous control system on the aforementioned small unmanned helicopter as is. Further, applying the autonomous control algorithms for the aforementioned conventional autonomous control system to the aforementioned small unmanned helicopter as is does not guarantee adequate control performance. Further, the calculation of a control instruction value is a time-consuming process due to the large number of computational steps involved in the determination of servo motor control reference values; consequently, when one attempts to achieve size reductions in the autonomous control system, one must contend with the conflicting requirements of accommodating a large number of computational steps and the stringent constraints imposed on the capabilities of the computational equipment and the size of the control program. Further, beyond the computational equipment, the sensors are also subject to stringent constraints on size and weight, which clearly adds difficulties to the construction of small and lightweight autonomous control systems. There has not been a successful development of an autonomous control system that can be mounted and flown on the type of small unmanned helicopter for which the present invention is intended.
The aforementioned conventional autonomous control system does not include a ground altitude sensor that detects the altitude of the helicopter with respect to the ground.
In such a case, it is impossible to detect the relative distance between the helicopter and the ground in real-time. Because a helicopter is a flying object that floats by rotating the main blade at high speeds to blow the wind toward the ground, it has the characteristic that its flying behavior netechnologies he ground is significantly different from that in the sky. Specifically, netechnologies he ground, compared with its behavior in the sky, the helicopter tends to be unstable in terms of orientation dynamic characteristics. Therefore, without a ground altitude sensor, it is impossible to smoothly control the helicopter's altitude so that its distance from the ground will remain constant or to perform automatic landing/take-off controls involving lifting off from the ground or descending to the ground.
For the implementation of autonomous control for an unmanned helicopter, it is desirable to install all of the minimum set of devices necessary for autonomous control on the aforementioned unmanned helicopter, which is a mobile station. The reason is that if a ptechnologies of the minimum necessary equipment is not mounted on the helicopter and intervention by the ground station is required, a feedback control loop would have to be provided between the ground station and the mobile station, which would require the provision of wireless communication intervals within the feedback loop. In such a case, if the wireless communications are cut off for any reason, the logical structure of the control system would collapse, which would not be desirable from the standpoint of safety during flight operations. On the other hand, the small unmanned helicopter addressed by the present invention is subject to stringent constraints on payload, which rules out the use of a sophisticated computer in the aforementioned computational unit for the aforementioned autonomous control system. Although the use of complex algorithms may be required as autonomous control algorithms, in such a case, it would be fortuitous if a sophisticated computer provided on the ground station can be used in conjunction with the aforementioned computational unit. However, there have not been cases where autonomous control systems that permit the combined use of a computational unit built into an autonomous control system and a computer on the ground station for autonomous control algorithm computation purposes have been developed.
The hobby radio-controlled helicopter of the class including the small unmanned helicopter addressed by the present invention incorporates commercially available servo motors and manual operation transmitters/receivers that have been in use for a long time and that have adequate track records. For the implementation of autonomous control for the aforementioned small unmanned helicopter, it is also advantageous from safety and compatibility standpoints to use these commercially available servo motors and manual operation transmitters/receivers. However, for hobby radio-controlled helicopters, such products are designed based upon the assumption that an operator maneuvers the helicopter manually. Although manual operation is essential for backup purposes to deal with dangerous situations, the implementation of autonomous control requires that the servo motors receive autonomous control signals from the aforementioned autonomous control system. In other words, switching between manual operation signals and autonomous control signals is essential. However, no switching devices have been developed that specifically address the aforementioned servo motor for hobby-type products.
The manual operation transmitter for hobby purposes is provided with a function of receiving external operation signals that permit beginning operators to practice piloting. When a ground station computer is used for the computation of autonomous control algorithms in the autonomous control system for the aforementioned small unmanned helicopter, it is possible to drive the aforementioned servo motors for the aforementioned small unmanned helicopter by providing autonomous control computation results as external operation signals to the aforementioned manual operation transmitter. However, the aforementioned manual operation transmitter can only accept the aforementioned external operation signals that are encoded in pulse format. Therefore, the aforementioned autonomous control computational results need to be converted into the pulse format. However, no conversion equipment that can be directly connected to the aforementioned ground station computer have been developed.
The so-called hobby-oriented radio-controlled helicopter, which belongs to the class of small unmanned helicopters addressed by the present invention, incorporates off-the-shelf servo motors and a manual operation transceiver, which have been in use for years and which have an adequate track record. For safety and compatibility, it is beneficial to use these off-the-shelf servo motors and manual operation transceivers in implementing autonomous control in the aforementioned small unmanned helicopter. However, hobby-oriented radio-controlled helicopters as products are designed under the assumption that they are manually operated by the operator. Since manual operation is the life line in the event of an emergency situation during autonomous control, it is essential for backup purposes. On the other hand, the implementation of autonomous control requires the severance of manual operation signals so that autonomous control signals are transmitted from the control unit to the servo motors. However, physically cutting off the signal line in order to sever manual operation signals would completely disable manual operation. Therefore, it is essential to be able to switch between the manual operation signals and the autonomous control signals. However, there have been no examples of switching units being developed for switching the aforementioned servo motors as hobby-oriented products. Whereas the conventional unmanned helicopter provides a similar switching function internally in a system that is mounted on the helicopter, employing similar means in the present invention would result in disadvantages in terms of the safety and reliability of the autonomous small unmanned helicopter and the compatibility with the hobby-oriented radio-controlled helicopter. A prerequisite to solving this problem is the concept of treating the aforementioned autonomous control unit as an add-in unit for the hobby-oriented radio-controlled helicopter, and separating this unit from the aforementioned small unmanned helicopter and from its aforementioned manual operation system. To this end, the aforementioned servo pulse mixing/switching unit, which would be functionally highly related to the hobby-oriented manual operation system, should be implemented as a stand-alone external unit separate from the aforementioned autonomous control unit.
With the conventional autonomous unmanned helicopter, the sole objective is to provide autonomous control of the helicopter; no consideration is given to situations in which autonomous control is inserted into manual operation by a human operator. The present invention is based on the concept of using an autonomous control unit as an auxiliary system for manual operation, i.e., as an operator-assist unit, beyond simply implementing autonomous controls. Various objectives and techniques can be considered for achieving operational-assist. For example, if the objective is to help the human operator to achieve step-wise improvements in manual operation, in the initial stages of practicing helicopter maneuvering, the percentage of autonomous control should be set large, and this percentage should be reduced gradually so that, at the end, maneuvering by complete manual operation with the absence of autonomous control should be achieved. Therefore, in the aforementioned servo pulse mixing/switching unit, it would be convenient to provide and mix manual operation signals and autonomous control signals in an arbitrary proportion, to be output to the aforementioned servo motors. However, there have been no cases of developing devices or software capable of mixing manual operation signals and autonomous control signals in any proportion in this manner.
The aforementioned servo pulse mixing/switching unit is the key system in the operation system for the aforementioned small unmanned helicopter. If the power for the system is stopped during the flight, drive signals could not be output to the aforementioned servo motors, even if the power is being supplied to other units, such as the aforementioned autonomous control unit, the aforementioned manual operation receiver, or the aforementioned servo motors, with result that the crashing of the helicopter would be unavoidable, leading to a potentially fatal accident. Essential to the development of the aforementioned switching unit is the installation of a computer for pulse processing and computation purposes. It might appear that for improved reliability of the system, stable power supply batteries for the system should be provided independently. However, an increase in the number of batteries can lead to human error, such as overlooking a dead battery, forgetting to turn on the power supply switch, or wiring errors due to increased wiring complexity. Flying the helicopter under such conditions can directly result in an accident. In other words, the safety and reliability necessary for practical operations could not be assured. Therefore, at a minimum, the possibility of accidents occurring due to human error related to the power supply must be eliminated.
Since the aforementioned servo pulse mixing/switching unit is a key unit in the operation system for the aforementioned small unmanned helicopter, if the operation of this unit stops during the flight, the crashing of the helicopter will be unavoidable, potentially leading to a fatal accident. Therefore, barring physical damage, in other cases, consistent, normal operation of the unit must be guaranteed.
As described above, the aforementioned servo pulse mixing/switching unit shares the power supply system with the hobby-oriented servo motors and the manual operation receiver and it is always used in an integral manner with these components. Therefore, it is desirable for the unit to have a high degree of affinity to the manual operation system comprised of such components. Specifically, it is desirable that even when the aforementioned autonomous control system is not powered on or there is no wire connection between the aforementioned autonomous control system and this unit, manual operation is always possible by means of the same operating procedures as the hobby-oriented radio-controlled helicopter, and this is also necessary from the standpoint of maintaining compatibility with the hobby-oriented radio-controlled helicopter. However, there have been no examples of cases of development of an autonomous small unmanned helicopter capable of supporting manual operation without an autonomous control system.
Since manual operation is intrinsically independent from autonomous control, it can be thought of as being completely unrelated to autonomous control. However, in some cases, the process of designing an autonomous control algorithm may require the measurement of manual operation signals. The creation of mathematical models in the present invention involves the use of what is called system characterization, wherein the input signals that are entered into the aforementioned servo motors for the aforementioned small unmanned helicopter are associated with the output signals indicating the flying condition of the aforementioned small unmanned helicopter, the output signals being measured by the sensors that are installed in the aforementioned autonomous control system, and analyzing these data so as to obtain a mathematical model. The system characterization process requires the collection of input/output data while the aforementioned small unmanned helicopter is flying, and this process is called a characterization experiment. Conducting a characterization experiment requires the operation of the aforementioned servo motors by means of characterization input signals that are well suited for system characterization. In such a case, the use of characterization input alone can cause a significant tilt in the attitude of the aforementioned small unmanned helicopter or a sudden acceleration, potentially leading to an accident. Therefore, it is necessary to stabilize the motion of the aforementioned small unmanned helicopter by actuating the correction rudders by manual operation. However, because correction rudders are also considered to be a part of characterization input, the aforementioned manual operation signals must also be obtained as measurement data during the system characterization process.
As stated above, the present invention also takes into consideration the use of the aforementioned autonomous control system as an auxiliary system for manual operation, i.e., an operator assist unit. As an objective and technique of operation assistance, manual operation signals, for example, could be associated with target value input signals for the aforementioned autonomous control algorithm, so that drive signals that are actually output to the aforementioned servo motors are all used as autonomous control signals, which are the results of computation by the aforementioned autonomous control algorithm. In other words, although the human operator may have the illusion of operating the helicopter himself, in actuality, all the human operator does is provide motion commands, which are target values, to the aforementioned autonomous small unmanned helicopter, and in this method, the aforementioned autonomous control algorithm is computed upon receipt of the target values, and autonomous control is effected. Because this method permits the provision of target values to the aforementioned autonomous control algorithm without using the aforementioned ground station computer, it provides the significant benefit of enabling persons not versed in computer operations to safely fly the aforementioned small unmanned helicopter in a manner that takes advantage of autonomous control. Such an approach requires the new technique of associating the aforementioned manual operation signals with target values.
The development of autonomous control algorithms for the autonomous control of the aforementioned small unmanned helicopter requires mathematical models that describe the dynamic characteristics of the helicopter. The use of mathematical models permits the application of various control theories, which have been improved in recent years and whose effectiveness has been recognized, to the development of autonomous control algorithms, which should improve flight performance in situations in which the aforementioned small unmanned helicopter is controlled autonomously.
However, the dynamic characteristics of a helicopter are subject to a complex interplay of dynamic action and fluid dynamic action, which makes analysis an extremely difficult task.
Although a detailed analysis of the dynamic characteristics of manned helicopters has been pursued aggressively, but little detailed analysis has been performed with regard to helicopters of the size addressed in the present invention. In addition, there have been no reports on the dynamic characteristics of the aforementioned servo motors.
Even if a mathematical model that describes the dynamic characteristics of the aforementioned small unmanned helicopter in detail exists, if the mathematical model is highly complex, the development of an autonomous control algorithm will also be difficult. Autonomous control algorithms developed and based on complex mathematical models are generally complex and may not necessarily be appropriate for execution by a computer that is subject to stringent restrictions on its computational capabilities due to weight limitations. There is a system identification method that avoids theoretical analyses and draws inferences on the dynamic characteristics of a given physical system based on its input/output relationships. System identification requires the input of signals containing frequency components encompassing a broad bandwidth into the physical system. However, entering such signals into the aforementioned small unmanned helicopter involves risk. In addition, such a system will also require devices for the measurement of the aforementioned input/output signals and an instrumentation system. There have been no cases in which system identification is run on the type of small unmanned helicopter addressed in the present invention and in which the soundness of the characterization model thus obtained is validated.